16 A. ©. OUDEMANS. 
of the two lateral lacunez, the transverse bands which separate 
them being here and there interrupted. 
The two great lateral lacune are surrounded by a thin layer 
of transverse muscular fibres. Still, I am inclined to call 
these spaces ‘‘lacune,” reserving the name of vessel for those 
that are in transverse section of a circular ellipsoidal shape. 
Bands of dorso-ventral muscles traverse the lacune, slanting 
backwards or forwards. They are so strongly inclined, that in 
transverse sections of ;+, mm. I never saw a band from one 
wall to the other, but always found it cut off, so that in section 
they resembled finger-like protuberances from the walls. 
Bands which were twice cut through thus produced in sections 
an insular patch in the lacune. McIntosh gives a similar 
description of this arrangement in his “Great Canadian 
Carinella” (25). 
As in Cephalotrix, I have here found a very thin layer of 
hyaline basal tissue, against which on the inner surface are 
found very distinct small round or ellipsoidal cells, with rela- 
tively large nuclei. 
We now follow the lacune backwards. We have passed 
the supra-proboscidian commissure of the brain, and have seen 
that the supra-proboscidian lacuna, which occurs only in some 
individuals, is already coalesced with the other, and dis- 
appears. 
Now, in those specimens which have a lacuna above the 
proboscidian sheath, there is also a lacuna below it. This, too, 
is wide and flattened, and becomes visible all at once, it 
evidently terminates blindly in front. The blind end lay in 
the same slice, wherein the infra-proboscidian commissure of 
the brain became visible. Close behind this region the inner- 
vation of the proboscis by two large nerve-trunks becomes 
visible. Just behind these the lacuna dilates, and then 
appears a broad arch (turned downwards) as a commu- 
nication between these three lacunz. This broad arch also 
is now and then traversed by large bands of transverse 
muscles. 
lt appears to me that all these transverse bands can co- 
